The lives of cancer patients are being put at risk, experts say, as the NHS struggles to see people quickly enough.
Patients are meant to start cancer treatment within 62 days of it being suspected, but nowhere in the UK has achieved this for more than two years.
It means one in six patients is now waiting longer than they should, the BBC analysis of official figures found.
It comes as data in England showed last-minute cancellations of operations have hit an all-time high.
There were more than 25,000 late cancelled operations from January to March - the highest since records began in the mid-1990s.
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This came despite NHS bosses ordering the cancellation of many January operations in advance in an attempt to relieve the pressure on A&Es and stop surgery being scrapped at the last minute.
Ian Eardley, of the Royal College of Surgeons, said it showed just how difficult winter had been.
He said last-minute cancellations, which take place on the day or the day before, were "very distressing" for patients.
These cancellations cover both cancer patients and those waiting for other operations, such as knee and hip replacements.
What's been happening with cancer?
England last hit its key 62-day target in December 2015, while in Scotland you have to go back to the end of 2012.
Wales has been failing since 2008 and Northern Ireland has never met its target since it was set in 2009.
The continued struggle to hit the target has meant a growing number of patients are waiting over 62 days.
Fran Woodard, of Macmillan Cancer Support, said the situation was "extremely dispiriting".
"Long waits to start cancer treatment can make an already difficult time even more distressing and unbearable, while also raising the possibility of someone's health deteriorating further," she said.
The reasons behind the growing pressures on the cancer system are similar to those experienced in A&E and in planned operations.
The numbers needing treatment have been rising - there has been a 26% rise in cases since 2012-13.
There are also growing shortages of staff, with hospitals reporting problems recruiting cancer doctors and chemotherapy nurses in particular, while bottlenecks in getting diagnostic tests done have been reported.
Hospitals have also said they have begun to struggle to free up the intensive care beds needed for patients undergoing surgery, because of the growing numbers of emergency cases coming through the doors of A&E.
'My cancer was terminal by the time I got treatment'
Ronny Andrews, 64, waited eight months for treatment - four times longer than he should have.
Doctors discovered a tumour on his liver in January 2017, but by the time he was offered chemotherapy it was too late. His cancer was terminal.
He says he tries not to get angry, but believes he could have had another three or four years if he had got quicker treatment.
"I'm resigned to it now. This is it. I try to smile and get on with it. Death comes to us all."
Cardiff and Vale University Health Board, which was in charge of his care, said his cancer had been difficult to diagnose.
His initial biopsy was delayed and then when it did take place it had to be repeated.
He has only been given a few months to live.
Does the NHS have a plan?
The way the target is measured differs in each part of the UK, although all expect patients to be seen in 62 days once there is an urgent suspicion a patient may have cancer.
In England, 85% of patients are meant to be seen in that timeframe, whereas it is 95% in the rest of the UK.
In Scotland the core target incorporates those referred via screening as well as by GPs, whereas the core target in England only looks at cases raised by GPs.
Cancer has been made a priority by ministers in each nation.
England is half-way through its five-year cancer strategy, which is seeing a major upgrade in radiotherapy machines, extra staff being recruited and a new four-week target being introduced for diagnostic testing.
The most recent month, March, saw the nation record its best performance for two years.
A government spokesman said the delays were not acceptable, but added survival rates were improving and other cancer targets were being met.
While Wales has failed to hit its target since 2008, it is the only part of the UK that has enjoyed a rise in performance over the past five years.
Over the past 12 months, 87.3% of patients were seen in 62 days, up from 85.8% during the same period in 2012-13.
A Welsh government spokeswoman said this is happening even though cases continue to rise and treatment is "increasing in complexity".
A spokesman for the Department of Health in Northern Ireland said despite the failure to hit the target, cancer care continues to be one of the "highest priorities".
However, he acknowledged the performance was "disappointing" and said efforts were being made to speed up testing and scans so diagnosis could be made quickly.